fix: validate admin settings file target (#894)

lib/admin/settings.ts

@@ -125,7 +125,12 @@ let writableCache: boolean | null = null
 export function isSettingsWritable(): boolean {
     if (writableCache !== null) return writableCache
     try {
-        const dir = path.dirname(getSettingsPath())
+        const filePath = getSettingsPath()
+        if (fs.existsSync(filePath) && !fs.statSync(filePath).isFile()) {
+            writableCache = false
+            return writableCache
+        }
+        const dir = path.dirname(filePath)
         fs.mkdirSync(dir, { recursive: true })
         fs.accessSync(dir, fs.constants.W_OK)
         writableCache = true

tests/unit/admin-settings.test.ts

@@ -154,9 +154,9 @@ describe("isSettingsWritable", () => {
         expect(isSettingsWritable()).toBe(true)
     })
 
-    it("returns false for an unwritable path", () => {
+    it("returns false when the settings path is a directory", () => {
         _resetForTests()
-        process.env.SETTINGS_FILE = "/nonexistent-root-dir/settings.json"
+        process.env.SETTINGS_FILE = tmpDir
         expect(isSettingsWritable()).toBe(false)
     })
 })
@@ -170,7 +170,9 @@ describe("settings file on disk", () => {
             version: 1,
             values: { TEST_ADMIN_VAR: "secret" },
         })
-        const mode = fs.statSync(filePath).mode & 0o777
-        expect(mode).toBe(0o600)
+        if (process.platform !== "win32") {
+            const mode = fs.statSync(filePath).mode & 0o777
+            expect(mode).toBe(0o600)
+        }
     })
 })